The commercial fabrication of semiconductor chips is performed on silicon wafer substrates, which are typically four to twelve inches in diameter. There are often more than 100 processing steps in the fabrication of semiconductor chips including oxidation, diffusion, ion implantation, deposition of conductors and insulators, photolithography, and etching. Various conducting and insulating layers are deposited uniformly over the wafer to a thickness of a few microns.
In critical applications, certain new parts of semiconductor processing equipment need to be cleaned prior to installation and use in order to remove residual contamination from the machining or manufacturing process in order to achieve levels of cleanliness similar to the semiconductor wafer itself. Furthermore, after many wafers have been processed, the equipment used in the semiconductor processing process becomes contaminated, and therefore unusable. For example, in an etching machine, polymer deposits on the outer circumference of electrodes or chucks supporting the wafers until it becomes thick enough to interfere with the wafer""s contact with the electrode. This results in non-uniform etching across the wafer as well as missed transfers due to a wafer sticking to polymer buildup on the electrode. Non-uniformity exceeding seven percent is beyond some specified limits, in turn affecting side wall profile variance across the wafer. In addition, other components in the equipment chamber e.g. roofs/domes and liners are also coated with polymers and contaminants which contribute particles, metallic and organic impurities to the wafers. Therefore, it is then necessary to disassemble the parts in the equipment chamber and clean the individual parts.
Generally, semiconductor manufacturing plants employ specialized cleaning houses to have the semiconductor processing equipment parts cleaned. These cleaning houses typically clean the equipment by following xe2x80x9crecipes,xe2x80x9d given to them by the manufacture of the equipment. These recipes generally include information informing the cleaning house how to clean the parts. Since, there are many variations to the wafer processes, the polymer and contamination levels of a used chamber part is different, therefore, merely following one cleaning recipe does not always result in the part being cleaned. In addition, after following the cleaning recipe, a conventional cleaning house generally will not test the parts to ensure its cleanliness. In general, a conventional cleaning house has no idea as to the effectiveness of the cleaning process provided to them in the recipe.
The result of following cleaning recipes in this manner, is that many semiconductor parts are returned to the semiconductor manufacturing plant still contaminated with unacceptable levels of impurities. This results in contamination that may be transferred onto a wafer typically in the form of high particle counts, or in inoperable equipment that must again be disassembled for re-cleaning, thus further increasing the down time for the equipment.
In view of the forgoing, what is needed are methods and systems for enhanced cleaning and certification of semiconductor fabrication equipment. The methods should be flexible, and consistent enough to minimize or eliminate contamination from the equipment, to improve the mean time between cleanings (MTBC), to improve the number of RF hours run on a chamber set of parts and to reduce the downtime experienced by most semiconductor fabrication equipment.
With the ability to test and verify the effectiveness of cleaning procedures, new cleaning methods can be developed for critical chamber parts. Critical chamber parts are usually constructed from base materials such as ceramics (Al2O3, SiC, AlN) and quartz (SiO2). Chamber parts manufactured from these base materials are very expensive and are selected because of they are non-contaminating with respect to metallics, organics and particles. With new cleaning methods, these critical chamber parts can be effectively cleaned and recycled to reduce manufacturing cost.
Typically, in the prior art, relatively high concentrations of acids and other cleaning agents were used to clean parts. For example, a typical acid bath for quartz cleaning would include 1 part HF, 1 part HNO3, and 1 part H2O. Unfortunately, such high concentration solutions suffer from a number of drawbacks. For one, they can damage the surface of part being cleaned by scoring, etching, pitting, etc. Further, these high concentration solutions tend to be expensive, hazardous, and difficult to dispose of.
The present invention addresses these needs by providing a process for enhanced semiconductor fabrication equipment and parts cleaning. In one embodiment, a definition is determined that defines the characteristics for a clean part. Next, a part to be cleaned is tested to determine its incoming impurity levels. A cleaning process is then determined that is capable of reducing the incoming impurity levels for a particular part, depending on the type of base material the part is made from, the deposits on the part, and characteristics of adhesion, particle generation and reactivity. The appropriate cleaning process is then applied to the part so that it reduces the incoming level of impurities on the part, and tested to ensure that the part is clean. There are various types of impurities, but typically they fall into the categories of metals, particles, and organic organics.
Advantageously, one embodiment of the present invention reduces the cleaning defects by use of repeated testing of the impurity levels after each pass through the cleaning process. Moreover, by knowing the characteristics of a clean part through testing, the process of the present invention can achieve particular impurity level goals with increased accuracy, and the part can be certified to meet an actual specification based on either the need for cleanliness in the semiconductor process, or based on statistically significant test data. Finally, the process may be continuously optimized to further enhance the cleaning process by direct testing of the cleanliness of the part, by correlating to number of xe2x80x9caddedxe2x80x9d particles and RF hours that the parts can be used before particles increase to unacceptable limits, and ultimately by correlating to improved wafer yield.
Using the dual concepts of in-process testing of the cleanliness of a part for improved cleaning performance, and testing the cleaned part after the final cleaning, a cleaning method can be customized, optimized, and validated for each critical part.
Advantageously, dilute chemistries can be used in preferred embodiments of the present invention. This makes the cleaning process less expensive. Used chemicals are also easier to dispose of because the percentage of acids is much lower which also in turn makes it less hazardous. Additionally, there is less damage to the product. The present invention further includes methodologies to determine optimal chemistries which are effective, yet dilute.
These and other advantages of the present invention will become apparent upon a study of the following descriptions and related drawings.